Process for forming fine patterns

ABSTRACT

Fine patterns are formed by a process wherein a workpiece is spin coated with a heat-resistant resin layer, this resin layer is spin coated with an organotitanium or titanium oxide layer, a resist pattern is formed on the organotitanium or titanium oxide layer, the organotitanium or titanium oxide layer is etched by ion etching with the resist pattern as a mask, and finally, the resin layer is etched by using the etched organotitanium or titanium oxide layer as a mask.

BACKGROUND OF THE INVENTION

This invention relates to a process for forming fine semiconductorpatterns, and more particularly to such a fine pattern forming processwhich is especially suited for forming patterns with small dimensionsaround or less than 1 μm.

Hitherto, for forming patterns for magnetic bubble memories and othersemiconductor devices, the so-called photoetching technique has beenused in which a workpiece is etched through a resist pattern formedthereon. In practice of this photoetching technique, the resist layersare required to have a sufficient thickness to endure during the etchingwork. For instance, in case a 0.35 μm thick NiFe alloy layer is etchedby ion milling, a resist thickness of about 0.7 μm is required. On theother hand, the fact is observed that generally the smaller the resistthickness, the higher becomes the resolution of the resist pattern.Making the best use of this fact, a so-called tri-layer resist processhas been proposed in which mask patterns for etching are made by usingthin resist layers (J. M. Moran et al: J. Vac. Sci. Technol., 16(6),1620-1624 (1979)). According to this process, a resin layer is firstformed on a workpiece, then an inorganic intermediate layer is formed onsaid resin layer and a resist pattern is formed on said inorganic layer.The inorganic layer is etched with the resist pattern as a mask, andthen the resin layer is etched by, for instance, ion etching usingoxygen. In this ion etching, said inorganic layer can act as a masksince this inorganic layer has high durability to ion etching withoxygen. In conducting inorganic layer etching, the resist layers are notrequired to have a greater thickness than necessary to withstandetching, and usually a small resist thickness on the order of 0.2-0.3 μmis used.

Relating to the inorganic layer, Moran et al proposed an SiO₂ layerformed by CVD (chemical vapor deposition) while Endo et al disclosed anSi layer formed by vacuum deposition (see A Collection of PapersPresented at the 28th Conference of the Japan Society of AppliedPhysics, 1981, p. 370). These proposals, however, have drawbacks in thatan evacuating equipment is required and that the working process isprolonged.

To avoid these problems, a method using an SiO₂ layer formed by spincoating has been proposed (Matsui et al: A Collection of PapersPresented at the 29th Conference of Japan Society of Applied Physics,1982, p. 357). According to this method, an SiO₂ layer can be obtainedby spin coating a monomolecular type organosilicon compound and furtherapplying a heat treatment, and the process is greatly simplified.However, the SiO₂ layer obtained from this method is not quitesatisfactory in adhesion to the underlying resin layer and the topresist pattern. In case, for instance, a polyimide resin, which is aheat-resistant high polymeric resin, is used for the resin layer, theSiO₂ layer formed thereon by said method proves to be liable to crackingand no good layer can be obtained. Also, when a novolac resist AZ-1350-J(Shipley Company) is used as resist, the obtained resist layer is foundto be poor in adhesion to the underlying SiO₂ layer formed by saidmethod, resulting in separation of the resist pattern. Further, sincethe monomolecular organosilicon compounds are easily hydrolyzed, a riskis great of the coats being contaminated by alien matters(hydrolyzates).

SUMMARY OF THE INVENTION

The present invention is aimed at solving these problems of the priorart methods and, to this end, it provides a process for forming a finepattern having good adhesiveness to resist layers and free of any fearof contamination.

The present invention features the use of an organotitanium, anorganotantalum as the intermediate layer in said tri-layer resistprocess. These materials have good adhesiveness to polyimide resins andnovolac resists. The organotitanium and organotantalum vary in the rateof hydrolysis depending on the compound types, but there exist thosecompounds which are very low in the rate of hydrolysis.

In order to attain the said object, the present invention provides aprocess for forming a fine pattern comprising the steps of forming aresin layer on a workpiece, forming on said resin layer a layer of atitanium compound such as organotitanium or titanium oxide or a tantalumcompound, further forming on said layer of a titanium or tantalumcompound a resist pattern of a desired configuration, etching saidtitanium or tantalum compound layer using said resist pattern as a mask,and then etching said resin layer using the resulting titanium ortantalum compound layer as a mask.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) through 1(d) show a schematic of an embodiment of the finepattern forming process according to this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of this invention will be explained withreference to the accompanying drawings.

As shown in FIG. 1(a), a layer 2 of a resin, preferably a heat-resistantresin, is formed on a workpiece 1. In this embodiment, a polyimide resinsolution is spin coated on the workpiece and then a heat treatment isapplied thereon at 350° C. to obtain a 1 μm thick resin layer. The resinlayer 2 is then covered with an intermediate layer 3 of organotitanium.The term "organotitanium" is used here to refer to a compound of Ti, C,O, H and such. In this embodiment, ATOLON NTi (Nippon Soda Co., Ltd.) isused as the organotitanium solution, and it is spin coated on the resinlayer 2, followed by a heat treatment at 200° C. to obtain a 0.1 μmthick organotitanium layer.

Then, a resist pattern 4 is formed on the intermediate organotitaniumlayer 3 as shown in FIG. 1(b). Used as resist in this embodiment is RD2000-N (Hitachi Chemical Co., Ltd.) which is a resist for deepultraviolet light, and it is subjected to contact exposure using deepultraviolet light to form a pattern. The resist thickness is 0.25 μm.

Then, the organotitanium is ion etched with a CF₄ gas as shown in FIG.1(c). This organotitanium etching can be done by approximately 5-minuteion etch at an input of 100 W under a vacuum of 5×10⁻³ Torr.

Finally, the resin layer is ion etched with oxygen gas as shown in FIG.1(d), at an input of 100 W under a vacuum of 5×10⁻³ Torr. The etchingrates of the resin layer (polyimide) and the organotitanium are 1,000Å/min and 10 Å/min, respectively, which indicates that theorganotitanium functions as a mask for ion etching of the resin layerwith oxygen gas.

Said sequence of processing steps gives a mask pattern for etching ofthe workpiece. A practical example of etching using said mask patternfor forming a magnetic bubble memory is described below.

A mask pattern made from an organotitanium and a polyimide layer isformed on a layer of Permalloy in the same way as in the above-describedembodiment. Then, the Permalloy is etched by ion milling. The etchingrates of said organotitanium, polyimide and Permalloy are 100 Å/min, 250Å/min and 220 Å/min, respectively, and the time required for etching the3,500 Å thick Permalloy layer is about 16 minutes. As a result of thision etch, the organotitanium-polyimide mask pattern presents a situationwhere the organotitanium has disappeared while the polyimide resin stillremained in the pattern. Since this polyimide resin, unlike the ordinaryresist materials, has excellent heat resistance and is also chemicallystable, it presents no problem on pattern reliability even if it is notremoved from the pattern.

While the invention has been described by way of an embodiment usingorganotitanium as a layer material, the effect of this invention can beattained equally by using organotantalum in place of saidorganotitanium. These materials can be etched with a CF₄ gas, andespecially the etching rate in ion etch with oxygen is very low. Also,these materials are very small in hydrolysis rate and chemically stable,so that even if the solution of these materials are retained for a longtime, there is no fear of causing contamination of the pattern.

In the embodiment described above, the organotitanium layer, after spincoating, was baked at 200° C. At this baking temperature, the materialis still in a state of organic matter. When the baking temperaturebecomes 400° C., the material is made into an inorganic matter and comesto have a compositional structure close to TiO₂. Even if a layer of suchTiO₂ -analogous structure is used, it is possible to conduct the sameprocess as above-described embodiment without damaging the said effectand advantages of the invention.

According to this invention, since the tri-layer resist structure iswholy made up of the spin coated layers as described above, the processcan be greatly simplified. Also, the organotitanium, organotantalum usedas the intermediate layer has good adhesiveness to the resin, especiallypolyimide resin used for the underlying (first) layer. Said intermediatelayer material also shows good adhesion to the top resist pattern,especially novolac resist, and is very excellent in stability andreproducibility.

What is claimed is:
 1. A process for forming fine patterns whichcomprises(a) forming a resin layer on a workpiece; (b) forming on saidresin layer a layer of a titanium or tantalum compound; (c) forming onsaid titanium or tantalum compound layer a resist pattern having adesired configuration; and (d) etching said titanium or tantalumcompound layer using said resist pattern as a mask, and (e) etching saidresin layer using the resulting titanium or tantalum compound layer as amask.
 2. A process according to claim 1, wherein said titanium compoundis an organotitanium.
 3. A process according to claim 1, wherein saidtitanium compound is titanium oxide.
 4. A process according to claim 1,wherein said resin layer is a layer of a heat-resistant resin.
 5. Aprocess according to claim 4, wherein the heat-resistant resin ispolyimide.
 6. A process according to claim 1, wherein the etching ofsaid titanium or tantalum compound layer is conducted with an ionetching gas containing a CF₄ gas.
 7. A process according to claim 1,wherein the etching of said resin layer is conducted by ion etch usingoxygen gas.